Impact of Cleaning on Membrane Performance during Surface Water Treatment: A Hybrid Process with Biological Ion Exchange and Gravity-Driven Membranes

ABSTRACT: In this study, the hybrid biological ion exchange (BIEX) resin and gravity-driven membrane (GDM) process was employed for the treatment of coloured and turbid river water. The primary objective was to investigate the impact of both physical and chemical cleaning methods on ceramic and polymeric membranes in terms of their stabilised flux, flux recovery after physical/chemical cleaning, and permeate quality. To address these objectives, two types of MF and UF membranes were utilised (M1 = polymeric MF, M2 = polymeric UF, M3 = ceramic UF, and M4 = lab-made ceramic MF). Throughout the extended operation, the resin functioned initially in the primary ion exchange (IEX) region (NOM displacement with pre-charged chloride) and progressed to a secondary IEX stage (NOM displacement with bicarbonate and sulphate), while membrane flux remained stable. Subsequently, physical cleaning involved air/water backwash with two different flows and pressures, and chemical cleaning utilised NaOH at concentrations of 20 and 40 mM, as well as NaOCl at concentrations of 250 and 500 mg Cl2/L. These processes were carried out to assess flux recovery and identify fouling reversibility. The results indicate an endpoint of 1728 bed volumes (BVs) for the primary IEX region, while the secondary IEX continued up to 6528 BV. At the end of the operation, DOC and UVA254 removal in the effluent of the BIEX columns were 68% and 81%, respectively, compared to influent water. This was followed by 30% and 57% DOC and UVA254 removal using M4 (ceramic MF). The stabilised flux remained approximately 3.8–5.2 LMH both before and after the cleaning process, suggesting that membrane materials do not play a pivotal role. The mean stabilised flux of polymeric membranes increased after cleaning, whereas that of the ceramics decreased. Enhanced air–water backwash flow and pressure resulted in an increased removal of hydraulic reversible fouling, which was identified as the dominant fouling type. Ceramic membranes exhibited a higher removal of reversible hydraulic fouling than polymeric membranes. Chemical cleaning had a low impact on flux recovery; therefore, we recommend solely employing physical cleaning

Diffusive-thermal instabilities in unstrained H₂O-diluted syngas diffusion flames

ABSTRACT: A new version of the unstrained diffusion flame burner that can be operated with gaseous fuels containing high vapor content is introduced. Being a good approximation of the classical chambered diffusion flame solution, the flames generated are nominally unstrained, unlike common research burners where hydrodynamic effects are significant. This permits quantitative comparison with theoretical models that are often based on this simple configuration, and paves the way for fundamental experimental studies with vaporized fuels. In this paper, the capabilities of the new burner design are exploited to study diffusive-thermal instabilities (DTIs) in H2O-diluted H2-CO-CH4-CO2 mixtures. H2O dilution can be significant in biomass-derived syngas mixtures that are not cooled prior to combustion, and that are often burned directly to lower losses as waste heat and pollutant emission in practical combustors. Flammability limits are first presented for a broad range of fuel blends, where the destabilizing effect of H2O dilution is discussed. Instability maps in terms of the Damköhler number are then provided to illustrate the different types of superimposed cellular-pulsating instabilities that onset from the simultaneous presence of H2 with high diffusivity, and CO/CH4 with much lower mobility. The characteristics of these peculiar instabilities are highly dependent on the H2O dilution fraction, which increases both the fuel blend and oxidizer Lewis numbers. The degree of cellularity superimposed in the pulsating multi-fuel flame is reduced at higher water content, as the number of observed cells decreases. The opposite effect is observed on the pulsation frequency, which increases at higher water concentrations

Explainable ensemble learning predictive model for thermal conductivity of cement-based foam

ABSTRACT: Cement-based foam has emerged as a strong contender in sustainable construction owing to its superior thermal and sound insulation properties, fire resistance, and cost-effectiveness. To effectively use cement-based foam as a thermal insulation material, it is important to accurately predict its thermal conductivity. The current study aims at coining an accurate methodology for predicting the thermal conductivity of cement-based foam using state-of-the-art machine learning techniques. A comprehensive experimental dataset of 504 data points was developed and used for training ensemble learning models including XGBoost, CatBoost, LightGBM and Random Forest. The independent variables of this dataset affecting the thermal conductivity are the cast density, percentage of pozzolan, porosity, percentage of moisture, and duration of hydration in days. Using the Isolation Forest algorithm proved effective in detecting and eliminating outliers in the dataset. All the ensemble learning techniques explored in this study achieved superior predictive accuracy with a coefficient of determination greater than 0.98 on the test dataset. The influence of the input features on the thermal conductivity was visualized using the SHapley Additive exPlanations (SHAP) approach and individual conditional expectation (ICE) plots. The cast density had the greatest effect on thermal conductivity. The explainable machine learning models demonstrated superior accuracy, efficiency, and reliability in estimating the thermal insulation of cement-based foam, opening the door for wider acceptance of this material in sustainable energy efficient construction

A variable speed water-to-water heat pump model used for ground-source applications

ABSTRACT: The main objective of this study is to model variable speed water-to-water heat pumps (VSHP) and to examine the impact of the operation of such devices on ground heat exchanger sizing and energy consumption when they are used in ground-source applications. In the first part of the paper, a complete physics-based steady-state model of a variable-speed water-to-water heat pump is briefly presented. A performance map approach is also used by modifying an existing TRNSYS variable speed heat pump model to provide a minimum speed of operation and a better representation at part load. Simulation results over a heating season on a residential ground source VSHP indicate that the energy coverage (i.e. percentage of annual heat supplied by the heat pump) increases at a faster rate than the effect coverage (i.e. percentage of peak building heat supplied by the heat pump) for a small value of the effect coverage. For example, for an effect coverage of 60%, the energy coverage is ∼ 93%. It is also shown that the normalized length of the ground heat exchanger varies linearly up to an effect coverage of 60% where it is equal to 75% of the value encountered for an effect coverage of 100%